tensor.h

/*
 * Copyright (c) PyPTO Contributors.
 * This program is free software, you can redistribute it and/or modify it under the terms and conditions of
 * CANN Open Software License Agreement Version 2.0 (the "License").
 * Please refer to the License for details. You may not use this file except in compliance with the License.
 * THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND, EITHER EXPRESS OR IMPLIED,
 * INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.
 * See LICENSE in the root of the software repository for the full text of the License.
 * -----------------------------------------------------------------------------------------------------------
 */
#pragma once

#include <memory.h>
#include <stdint.h>

#include <algorithm>
#include <sstream>
#include <string>
#include <type_traits>
#include <utility>

#include "assert_compat.h"
#include "data_type.h"
#include "pto_task_id.h"

/**
 * Buffer Handle
 *
 * Represents a device memory buffer with address and total size in bytes.
 * This is the underlying memory allocation that a ChipTensor describes access patterns for.
 */
struct PTOBufferHandle {
    uint64_t addr;  // Device memory address (bytes)
    uint64_t size;  // Total buffer size in bytes
};

/**
 * TensorArgType - Distinguishes inputs, outputs, and in-place updates.
 *
 * A per-tensor tag carried by TaskArgs (drives dependency inference at submit
 * time; stripped before the args cross the dispatch boundary).
 */
enum class TensorArgType : int32_t {
    INPUT = 0,            // Read-only input buffer
    OUTPUT = 1,           // Write-only output buffer (runtime allocates)
    INOUT = 2,            // Read-then-write: modifier for downstream
    OUTPUT_EXISTING = 3,  // Write-only existing tensor: skips OverlapMap lookup, depends on creator
    NO_DEP = 4,           // No-dependency existing tensor: skips OverlapMap lookup, no publish
};

// `OverlapStatus` / `Segment` (overlap geometry) live in the runtime
// pto_tensormap.h. `TensorCreateInfo` (submit-time create-info for
// runtime-allocated outputs) and its materialization helpers live in the
// runtime tensor_create_info.h. Both are runtime-only and intentionally not
// part of the wire/host-facing ChipTensor definition.

/**
 * ChipTensor descriptor for Task input/output (128B = 2 cache lines)
 *
 * Describes a strided memory access pattern on Global Memory (GM) using:
 *   - `buffer`: underlying memory allocation (addr/size in bytes)
 *   - `start_offset`: 1D element offset of the view origin from `buffer.addr`
 *   - `shapes[i]`, `strides[i]`: per-dim view shape and **element** stride
 *
 * Stride semantics:
 *   - Element-granularity (matches start_offset). Byte offset of element
 *     `coords[]` is `(start_offset + Σ coords[i] · strides[i]) · dtype_bytes`.
 *   - strides[i] > 0 STRICTLY. Broadcast (stride=0) and negative slice step
 *     (stride<0) are NOT supported.
 *
 * Fast-path flags on cache line 1:
 *   - manual_dep: when true, dependency tracking is creator-only (skip OverlapMap)
 *   - is_contiguous: cached PyTorch-style contiguous flag — i.e.
 *     `strides[i] == prod(shapes[i+1..ndims-1])`. When true AND start_offset==0,
 *     all hot paths can compute extent_elem from `shapes` alone and never read
 *     cache line 2. NOTE: this is strictly tighter than the pre-#808
 *     `shapes[i] == raw_shapes[i]` test, but equivalent on every view the old
 *     (raw_shapes-based) encoding could express; the two only diverge on
 *     post-#808-only views (transpose / permute / slice-with-step results).
 *
 * Layout: cache line 1 holds hot-path fields (buffer, owner_task_id,
 * start_offset, version, ndims, dtype, flags, shapes); cache line 2 holds
 * stride + cached extent_elem.
 *
 * Construction:
 * Default construction is public (ChipTensor doubles as wire / TaskArgs / blob
 * storage, which needs a default-constructible element) but yields an
 * UNINITIALIZED object that must be filled before use. The parameterized
 * constructor is private, so a *valid* ChipTensor (real buffer, row-major strides)
 * is obtained only through controlled entry points:
 *   - make_tensor_external(...)
 *   - TaskOutputTensors returned by submit(...)
 *   - ChipTensor::view() / reshape() / transpose() / permute() / slice() on an existing valid ChipTensor
 */
struct alignas(64) ChipTensor {
    // === Cache line 1 (64B) — hot path ===
    PTOBufferHandle buffer;            // Underlying memory buffer (addr in bytes, size in bytes)
    PTO2TaskId owner_task_id;          // Creator task; PTO2TaskId::invalid() for external tensors
    uint64_t start_offset;             // 1D ELEMENT offset of the view origin into `buffer`
    int32_t version;                   // ChipTensor version for overlap detection
    uint32_t ndims;                    // Number of dimensions used
    DataType dtype;                    // Data type of tensor elements
    bool manual_dep;                   // True when dependency tracking is creator-only (skip OverlapMap lookup/insert)
    bool is_contiguous;                // Cached: strides[] == row_major_stride(shapes)
    AddressSpace address_space;        // HOST (default) or DEVICE (child-managed device memory; skips H2D copy)
    uint32_t shapes[MAX_TENSOR_DIMS];  // Current view shape per dimension (elements)

    // === Cache line 2 (64B) — warm path (view metadata) ===
    // Field order: place the 8B-aligned cache before the 4B-aligned strides[]
    // to avoid 4B padding between them (sizeof(ChipTensor) must stay 128).
    uint64_t extent_elem_cache;         // Cached extent_elem (see extent_elem()); maintained by ops
    uint32_t strides[MAX_TENSOR_DIMS];  // Element stride per dimension; ALWAYS > 0 (type-enforced)
    uint8_t _pad_cl2[36];               // Reserved for future extension

    // Default construction is public: ChipTensor doubles as the wire / TaskArgs
    // storage type (TaskArgsTpl<ChipTensor> arrays, ChipStorageTaskArgs POD, blob
    // memcpy targets), all of which require a default-constructible element. A
    // default-constructed ChipTensor is uninitialized and must be filled via
    // make_tensor_external() / init_external() / a view op before use.
    ChipTensor() = default;

    // --- Copy / move / destroy ---
    // Kept trivially copyable (default copy = byte-for-byte) so other modules
    // (PTO2TensorMapEntry::copy_from_tensor, TensorCreateInfo memcpy path)
    // can rely on memcpy semantics. The contiguous fast-path optimization
    // lives in `init(const ChipTensor&)`; call sites that care should use
    // `result.init(*this)` instead of the default copy ctor.
    ChipTensor(const ChipTensor &) = default;
    ChipTensor &operator=(const ChipTensor &) = default;
    ChipTensor(ChipTensor &&) = default;
    ChipTensor &operator=(ChipTensor &&) = default;
    ~ChipTensor() = default;

    // ========================================================================
    // Accessors / helpers
    // ========================================================================

    /// Number of logical elements covered by the view (NOT the extent).
    /// ndims > 0 is a construction-time invariant (see init_external /
    /// init_from_create_info), so the loop always runs at least once.
    uint64_t numel() const {
        uint64_t total = 1;
        for (uint32_t i = 0; i < ndims; i++)
            total *= shapes[i];
        return total;
    }

    /// Element extent — the smallest M such that every reachable element lies in [start_offset, start_offset+M).
    /// For strides[i]>0: extent_elem = 1 + Σ (shapes[i]-1) · strides[i].
    uint64_t extent_elem() const {
        if (is_contiguous) return numel();  // fast path: line 2 not needed when contiguous
        return extent_elem_cache;
    }

    /// True when `buffer.addr` is a device pointer allocated by the child process
    /// (host skips the H2D copy in init_runtime_impl). Host-side concept carried
    /// across the wire; runtime views inherit it via the cache-line-1 copy.
    [[nodiscard]] bool is_device_memory() const { return address_space == AddressSpace::DEVICE; }

    /// Logical byte size of the view (numel * element size). For a contiguous
    /// host-constructed tensor this equals buffer.size; provided for parity with
    /// the host-side allocators that size buffers from a tensor's logical bytes.
    [[nodiscard]] uint64_t nbytes() const { return numel() * get_element_size(dtype); }

    /// Typed pointer to the tensor's buffer base (== buffer.addr). Convenience
    /// accessor used by orchestration sources to read raw tensor data; matches
    /// the former ContinuousTensor::data_as<T>() semantics.
    template <typename T>
    T *data_as() const {
        return reinterpret_cast<T *>(static_cast<uintptr_t>(buffer.addr));
    }

    // ========================================================================
    // Initialization (operates on already-constructed ChipTensor)
    // ========================================================================

    /// Initialize as a contiguous tensor that covers `shapes[]` starting at `addr`.
    /// stride is set to row_major(shapes); start_offset = 0; is_contiguous = true.
    /// Enforces the ndims > 0 invariant relied upon by every downstream op.
    void init_external(
        void *addr, uint64_t buffer_size_bytes, const uint32_t in_shapes[], uint32_t in_ndims, DataType in_dtype,
        int32_t in_version, bool in_manual_dep = false, AddressSpace in_address_space = AddressSpace::HOST
    ) {
        always_assert(in_ndims > 0 && in_ndims <= MAX_TENSOR_DIMS);
        buffer = {reinterpret_cast<uint64_t>(addr), buffer_size_bytes};
        ndims = in_ndims;
        dtype = in_dtype;
        version = in_version;
        manual_dep = in_manual_dep;
        is_contiguous = true;
        address_space = in_address_space;
        start_offset = 0;
        owner_task_id = PTO2TaskId::invalid();
        // Single reverse pass: write shapes, accumulate row-major stride, and
        // track numel — `s` ends as prod(shapes) which is also extent_elem
        // for a contiguous view.
        uint32_t s = 1;
        for (int32_t i = static_cast<int32_t>(in_ndims) - 1; i >= 0; --i) {
            shapes[i] = in_shapes[i];
            strides[i] = s;
            s *= in_shapes[i];
        }
        extent_elem_cache = s;
    }

    /// Deep copy with contiguous fast-path optimization.
    ///
    /// Always copies cache line 1 (always needed: buffer, shapes, dtype, ...).
    /// When `other` is in canonical contiguous form (is_contiguous &&
    /// start_offset == 0), cache line 2 (stride / extent_elem_cache) is fully
    /// derivable from line 1, so we **skip reading other's cache line 2** and
    /// write dst's line 2 from the local shapes instead. Non-contiguous source
    /// pays one line 2 read; contiguous source does not.
    void init_from(const ChipTensor &other) {
        init_from_line1(other);
        if (other.is_contiguous && other.start_offset == 0) {
            // Derive line 2 from line 1: stride = row-major of shapes; extent = numel.
            uint32_t s = 1;
            for (int32_t i = static_cast<int32_t>(ndims) - 1; i >= 0; --i) {
                strides[i] = s;
                s *= shapes[i];
            }
            extent_elem_cache = s;
        } else {
            extent_elem_cache = other.extent_elem_cache;
            for (uint32_t i = 0; i < other.ndims; i++) {
                strides[i] = other.strides[i];
            }
            // _pad_cl2 left stale on purpose — reserved bytes are not
            // semantically read by any consumer.
        }
    }

    /// View ops use this: copy cache line 1 only, leaving cache line 2 (stride,
    /// extent_elem_cache) untouched. The op then mutates shapes / start_offset
    /// in place and calls `refresh_derived()` to recompute line 2 once. This
    /// avoids the wasted line 2 writes that `init_from()` would do just before
    /// the op overwrites them.
    void init_from_line1(const ChipTensor &other) { memcpy(this, &other, 64); }

    /// Backward-compat alias used by orchestrator hot paths that need a full
    /// deep copy. Equivalent to `init_from(other)`.
    void copy(const ChipTensor &other) { init_from(other); }

    // Materialization from a TensorCreateInfo (runtime-allocated outputs) lives
    // in the runtime tensor_create_info.h as the free functions
    // init_tensor_from_create_info() / fill_tensor_initial_value(); they operate
    // on a ChipTensor& through its public members. Kept out of the wire/host-facing
    // ChipTensor so this header has no dependency on the runtime-only create-info.

    // ========================================================================
    // Address / offset computation
    // ========================================================================

    /// Compute 1D flat ELEMENT offset of `indices[]` from `buffer.addr`.
    /// Callers multiply by `get_element_size(dtype)` to obtain a byte offset.
    /// Works for any view (transpose / permute / slice / reshape).
    uint64_t compute_flat_offset(const uint32_t indices[], uint32_t in_ndims) const {
        uint64_t elem_off = start_offset;
        for (uint32_t d = 0; d < in_ndims; d++) {
            elem_off += static_cast<uint64_t>(indices[d]) * static_cast<uint64_t>(strides[d]);
        }
        return elem_off;
    }

    // ========================================================================
    // View operations (zero-copy metadata rewrites)
    // ========================================================================

    /// Sub-tensor at per-dim offsets, with new per-dim shape.
    /// Updates start_offset += Σ off[i]·strides[i]; shapes := new_shape; stride unchanged.
    /// Each (offset[i], new_shape[i]) must stay within the current shapes[i] —
    /// i.e. a view cannot expand any dimension beyond what the parent view sees.
    /// Exception: a zero-size view (any new_shape[i] == 0) captures no bytes,
    /// so out-of-range offsets are harmless and accepted as a no-op. Codegen
    /// relies on this to clamp dynamic context-length / sequence-position
    /// offsets that can run past the parent tensor — it emits guards of the
    /// form ``(off >= shape ? 0 : min(...))`` to set the SHAPE dim and leaves
    /// the OFFSET dim as the raw (possibly out-of-range) value, expecting the
    /// runtime to honour the empty-view contract.
    ChipTensor view(const uint32_t view_shapes[], const uint32_t view_offsets[], bool in_manual_dep = false) const {
        ChipTensor result;
        // Copy line 1 only; stride from *this is still in result's line 2 garbage
        // — we need to bring it forward explicitly since view keeps stride.
        result.init_from_line1(*this);
        bool empty = false;
        for (uint32_t i = 0; i < ndims; i++) {
            if (view_shapes[i] == 0) {
                empty = true;
                break;
            }
        }
        for (uint32_t i = 0; i < ndims; i++) {
            if (!empty) {
                debug_assert(view_offsets[i] + view_shapes[i] <= shapes[i]);
                result.start_offset += static_cast<uint64_t>(view_offsets[i]) * static_cast<uint64_t>(strides[i]);
            }
            result.shapes[i] = view_shapes[i];
            result.strides[i] = strides[i];
        }
        result.manual_dep = in_manual_dep;
        result.refresh_derived();
        if (empty) {
            result.is_contiguous = true;
            result.extent_elem_cache = 0;
        } else {
            result.assert_in_buffer_bounds();
        }
        return result;
    }

    bool valid_transpose(uint32_t x, uint32_t y) const { return x < ndims && y < ndims; }

    /// Swap two dimensions: shapes/stride swapped together. start_offset unchanged.
    ChipTensor transpose(uint32_t x, uint32_t y, bool in_manual_dep = false) const {
        debug_assert(valid_transpose(x, y));
        ChipTensor result;
        result.init_from_line1(*this);
        // Carry forward source's stride before swapping (line 2 was not memcpy'd).
        for (uint32_t i = 0; i < ndims; i++)
            result.strides[i] = strides[i];
        std::swap(result.shapes[x], result.shapes[y]);
        std::swap(result.strides[x], result.strides[y]);
        result.manual_dep = in_manual_dep;
        result.refresh_derived();
        return result;
    }

    /// Permute dimensions according to `order[]` (length = ndims).
    /// Both shapes and stride are reordered in-place; start_offset unchanged.
    ChipTensor permute(const uint32_t order[], bool in_manual_dep = false) const {
        ChipTensor result;
        result.init_from_line1(*this);
        for (uint32_t i = 0; i < ndims; i++) {
            debug_assert(order[i] < ndims);
            result.shapes[i] = shapes[order[i]];
            result.strides[i] = strides[order[i]];
        }
        result.manual_dep = in_manual_dep;
        result.refresh_derived();
        return result;
    }

    /// Slice dimension `dim` with `[start, end)` and positive `step`.
    /// strides[dim] *= step; shapes[dim] = ⌈(end-start)/step⌉; start_offset += start·strides[dim_old].
    ChipTensor slice(uint32_t dim, uint32_t start, uint32_t end, uint32_t step = 1, bool in_manual_dep = false) const {
        debug_assert(dim < ndims);
        debug_assert(step >= 1);
        debug_assert(end > start);
        debug_assert(end <= shapes[dim]);
        ChipTensor result;
        result.init_from_line1(*this);
        // Carry forward source's stride before patching the sliced dim.
        for (uint32_t i = 0; i < ndims; i++)
            result.strides[i] = strides[i];
        const uint32_t old_stride_d = strides[dim];
        result.start_offset += static_cast<uint64_t>(start) * static_cast<uint64_t>(old_stride_d);
        const uint32_t new_len = (end - start + step - 1) / step;
        result.shapes[dim] = new_len;
        result.strides[dim] = static_cast<uint32_t>(static_cast<uint64_t>(old_stride_d) * step);
        result.manual_dep = in_manual_dep;
        result.refresh_derived();
        result.assert_in_buffer_bounds();
        return result;
    }

    bool valid_reshape(const uint32_t new_shapes[], uint32_t new_ndims) const {
        uint64_t x = numel();
        uint64_t y = 1;
        for (uint32_t i = 0; i < new_ndims; i++)
            y *= new_shapes[i];
        return x == y;
    }

    /// Reshape — zero-copy only if source is_contiguous; otherwise asserts.
    /// Materialize fallback (allocating a contiguous copy) is NOT in this op;
    /// callers must reach contiguous via a copy before calling reshape on a
    /// non-contiguous view.
    ChipTensor reshape(const uint32_t new_shapes[], uint32_t new_ndims, bool in_manual_dep = false) const {
        debug_assert(valid_reshape(new_shapes, new_ndims));
        always_assert(is_contiguous);
        ChipTensor result;
        result.init_from_line1(*this);
        result.ndims = new_ndims;
        result.manual_dep = in_manual_dep;
        // Single reverse pass: write new shapes, accumulate row-major stride, track numel.
        uint32_t s = 1;
        for (int32_t i = static_cast<int32_t>(new_ndims) - 1; i >= 0; --i) {
            result.shapes[i] = new_shapes[i];
            result.strides[i] = s;
            s *= new_shapes[i];
        }
        result.is_contiguous = true;
        result.extent_elem_cache = s;
        return result;
    }

    // ========================================================================
    // Dump for diagnostics
    // ========================================================================

    std::string dump() const {
        std::stringstream ss;
        std::string indent = "    ";
        ss << "{" << '\n';
        ss << indent << "buffer.addr: " << buffer.addr << '\n';
        ss << indent << "buffer.size: " << buffer.size << " bytes" << '\n';
        ss << indent << "dtype: " << get_dtype_name(dtype) << '\n';
        ss << indent << "ndims: " << ndims << '\n';
        ss << indent << "version: " << version << '\n';
        ss << indent << "start_offset: " << start_offset << " (elements)" << '\n';
        ss << indent << "is_contiguous: " << (is_contiguous ? "true" : "false") << '\n';
        ss << indent << "shapes: [";
        for (uint32_t i = 0; i < ndims; i++) {
            if (i > 0) ss << ", ";
            ss << shapes[i];
        }
        ss << "]" << '\n';
        ss << indent << "strides: [";
        for (uint32_t i = 0; i < ndims; i++) {
            if (i > 0) ss << ", ";
            ss << strides[i];
        }
        ss << "]" << '\n';
        ss << "}" << '\n';
        return ss.str();
    }

private:
    // The parameterized constructor is private: a fully-initialized ChipTensor with
    // a real buffer comes only through make_tensor_external() / view ops. (The
    // default constructor is public — see above — for POD/array storage.)
    ChipTensor(
        void *addr, uint64_t buffer_size_bytes, const uint32_t in_shapes[], uint32_t in_ndims, DataType in_dtype,
        int32_t in_version, bool in_manual_dep = false, AddressSpace in_address_space = AddressSpace::HOST
    ) {
        init_external(
            addr, buffer_size_bytes, in_shapes, in_ndims, in_dtype, in_version, in_manual_dep, in_address_space
        );
    }

    // ------------------------------------------------------------------------
    // Internal helpers
    // ------------------------------------------------------------------------

    /// Recompute extent_elem_cache and is_contiguous from current shapes / stride.
    /// Called after any op that mutates view metadata. Single reverse pass:
    ///   extent_elem += (shapes[i] - 1) · strides[i]
    ///   is_contiguous &&= (strides[i] == prod(shapes[i+1..]))
    void refresh_derived() {
        uint64_t e = 1;
        uint64_t expected = 1;
        bool contig = true;
        for (int32_t i = static_cast<int32_t>(ndims) - 1; i >= 0; --i) {
            if (strides[i] != expected) contig = false;
            if (shapes[i] > 0) {
                e += static_cast<uint64_t>(shapes[i] - 1) * static_cast<uint64_t>(strides[i]);
            }
            expected *= shapes[i];
        }
        extent_elem_cache = e;
        is_contiguous = contig;
    }

    /// Assert the view stays inside the underlying buffer (byte-range safety).
    void assert_in_buffer_bounds() const {
        const uint64_t elem_size = get_element_size(dtype);
        const uint64_t buffer_elems = buffer.size / elem_size;
        debug_assert(start_offset + extent_elem_cache <= buffer_elems);
    }

    // Friends that need to construct ChipTensors
    friend struct PTO2TaskPayload;
    friend inline ChipTensor make_tensor_external(
        void *addr, const uint32_t shapes[], uint32_t ndims, DataType dtype, bool manual_dep, int32_t version,
        AddressSpace address_space
    );
    friend inline ChipTensor make_tensor_strided(
        void *addr, const uint32_t shapes[], const uint32_t strides[], uint32_t ndims, DataType dtype, bool manual_dep,
        int32_t version, AddressSpace address_space
    );
};

static_assert(
    std::is_trivially_copyable_v<ChipTensor>, "ChipTensor must be trivially copyable for DMA / wire transport"
);
static_assert(sizeof(ChipTensor) == 128, "ChipTensor must be exactly 2 cache lines (128 bytes)");
static_assert(offsetof(ChipTensor, owner_task_id) == 16, "owner_task_id must be at bytes 16-23 (cacheline 1)");
static_assert(offsetof(ChipTensor, start_offset) == 24, "start_offset must be at bytes 24-31 (cacheline 1)");
static_assert(offsetof(ChipTensor, version) == 32);
static_assert(offsetof(ChipTensor, ndims) == 36);
static_assert(offsetof(ChipTensor, dtype) == 40);
static_assert(offsetof(ChipTensor, manual_dep) == 41);
static_assert(offsetof(ChipTensor, is_contiguous) == 42);
static_assert(offsetof(ChipTensor, address_space) == 43, "address_space must be at byte 43 (cacheline 1)");
static_assert(offsetof(ChipTensor, shapes) == 44, "shapes must start at byte 44 (cacheline 1)");
static_assert(offsetof(ChipTensor, extent_elem_cache) == 64, "extent_elem_cache must start at byte 64 (cacheline 2)");
static_assert(offsetof(ChipTensor, strides) == 72);

// =============================================================================
// ChipTensor factory — canonical construction entry for pre-allocated external
// memory. Lives here (not in the runtime orchestration header) so host-side
// consumers (the nanobind binding, make_chip_tensor_arg) build ChipTensors through the
// same controlled path as the runtime. The resulting ChipTensor is contiguous:
// start_offset == 0 and strides == row_major(shapes).
// =============================================================================
inline ChipTensor make_tensor_external(
    void *addr, const uint32_t shapes[], uint32_t ndims, DataType dtype = DataType::FLOAT32, bool manual_dep = false,
    int32_t version = 0, AddressSpace address_space = AddressSpace::HOST
) {
    uint64_t total = 1;
    for (uint32_t i = 0; i < ndims; i++) {
        total *= shapes[i];
    }
    return {addr, total * get_element_size(dtype), shapes, ndims, dtype, version, manual_dep, address_space};
}

// =============================================================================
// ChipTensor factory — a possibly-strided external view. `addr` is the view origin
// (start_offset == 0); `strides[]` are element strides (may be non-row-major, as
// from a transpose / permute / step-sliced Tensor). Derived fields
// (extent_elem_cache, is_contiguous) are recomputed from shapes + strides;
// buffer.size is the element extent in bytes.
// =============================================================================
inline ChipTensor make_tensor_strided(
    void *addr, const uint32_t shapes[], const uint32_t strides[], uint32_t ndims, DataType dtype = DataType::FLOAT32,
    bool manual_dep = false, int32_t version = 0, AddressSpace address_space = AddressSpace::HOST
) {
    always_assert(ndims > 0 && ndims <= MAX_TENSOR_DIMS);
    ChipTensor t{};
    t.buffer.addr = reinterpret_cast<uint64_t>(addr);
    t.ndims = ndims;
    t.dtype = dtype;
    t.version = version;
    t.manual_dep = manual_dep;
    t.address_space = address_space;
    t.start_offset = 0;
    t.owner_task_id = PTO2TaskId::invalid();
    for (uint32_t i = 0; i < ndims; i++) {
        t.shapes[i] = shapes[i];
        t.strides[i] = strides[i];
    }
    t.refresh_derived();  // extent_elem_cache + is_contiguous from shapes/strides
    t.buffer.size = t.extent_elem_cache * get_element_size(dtype);
    return t;
}